FIX #1465, error messages could sometimes say things like "A.T doesn't match A.T"
This turned out to be a black hole, however we believe we now have a plan that does the right thing and shouldn't need to change again. Error messages will only ever refer to a name in an unambiguous way, falling back to <package>:<module>.<name> if no unambiguous shorter variant can be found. See HscTypes.mkPrintUnqualified for the details. Earlier hacks to work around this problem have been removed (TcSimplify).